(2‐Hydroxy isobutyric) acid containing poly(glycolic acid): Structure–properties relationship

Poly(glycolic acid) (PGA) and a series of novel random copolymers of PGA containing 2‐hydroxyisobutyrric acid (PGAPHIB) (HIB unit content from 1.5 to 7.4 mol %) were synthesized and characterized in terms of chemical structure and molecular weight. Afterward, the polyesters were examined by thermogravimetric analysis, differential scanning calorimetry, and X‐ray diffraction techniques. The copolymers, which displayed a better thermal stability than PGA, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PGA. Baur's equation described well the T_m‐composition data. X‐ray diffraction measurements allowed the identification of the PGA crystalline structure in all cases. After melt quenching, semicrystalline samples were obtained with the exception of PGAPHIB7.4 copolymer. The introduction of HIB units decreased the crystallization rate compared with pure PGA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1901–1910, 2010     

The Direction of Time: From the Global Arrow to the Local Arrow

In this paper we discuss the traditional approaches to the problem of the arrow of time. On the basis of this discussion we adopt a global and nonentropic approach, according to which the arrow of time has a global origin and is an intrinsic, geometrical feature of space-time. Finally, we show how the global arrow is translated into local terms as a local time-asymmetric flux of energy.     

The dynamics of a thin spherically-symmetric radiating shell

The conclusions of paper [2] are modified: using the shell formalism, relativistic effect could eventually be detected in X-ray bursters.     

Oxidative Deselenization of Selenocysteine: Applications for Programmed Ligation at Serine

Despite the unique chemical properties of selenocysteine (Sec), ligation at Sec is an under‐utilized methodology for protein synthesis. We describe herein an unprecedented protocol for the conversion of Sec to serine (Ser) in a single, high‐yielding step. When coupled with ligation at Sec, this transformation provides a new approach to programmed ligations at Ser residues. This new reaction is compatible with a wide range of functionality, including the presence of unprotected amino acid side chains and appended glycans. The utility of the methodology is demonstrated in the rapid synthesis of complex glycopeptide fragments of the epithelial glycoproteins MUC5AC and MUC4 and through the total synthesis of the structured, cysteine (Cys)‐free protein eglin C.     

Nickel‐Catalyzed Barton Decarboxylation and Giese Reactions: A Practical Take on Classic Transforms

Two named reactions of fundamental importance and paramount utility in organic synthesis have been reinvestigated, the Barton decarboxylation and Giese radical conjugate addition. N ‐hydroxyphthalimide (NHPI) based redox‐active esters were found to be convenient starting materials for simple, thermal, Ni‐catalyzed radical formation and subsequent trapping with either a hydrogen atom source (PhSiH₃) or an electron‐deficient olefin. These reactions feature operational simplicity, inexpensive reagents, and enhanced scope as evidenced by examples in the realm of peptide chemistry.     

Generalized asymptotic functions in nonconvex multiobjective optimization problems

In this paper, we use generalized asymptotic functions and second-order asymptotic cones to develop a general existence result for the nonemptiness of the proper efficient solution set and a sufficient condition for the domination property in nonconvex multiobjective optimization problems. A new necessary condition for a point to be efficient or weakly efficient solution is given without any convexity assumption. We also provide a finer outer estimate for the asymptotic cone of the weakly efficient solution set in the quasiconvex case. Finally, we apply our results to the linear fractional multiobjective optimization problem.     

Exploring the heteroatom effect on polyelectrolyte multilayer assembly: the neglected polyoniums

Different positive polyelectrolytes having the same charge density, molecular weight, and molecular weight distribution were employed for polyelectrolyte multilayer (PEMU) assembly. The polycations differed only in the heteroatom on which the positive charge resided: poly(vinyl benzyl trimethyl ammonium) chloride, poly(vinyl benzyl trimethyl phosphonium) chloride, and poly(vinyl benzyl dimethyl sulfonium) chloride. While the ammonium repeat unit has been employed on numerous occasions for PEMU assembly, the phosphonium and sulfonium units are relatively neglected. The polyanions, poly(styrene sulfonate), PSS, or poly(acrylic acid), PAA, were typical pH-independent or pH-dependent polymers, respectively. All three polyoniums were quite similar in showing linear layer-by-layer buildup with PSS and exponential growth with PAA, under the conditions employed. Hydration and wettability were also similar between polyoniums.